Particular embodiments generally relate to methods, apparatus, and algorithms for detecting the presence or use of a bidirectional triode thyristor, commonly known in the industry as a triode for alternating current (TRIAC) device, for controlling light emitting diodes (LED).
Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Many industrial and commercial applications use various types of light sources for illuminating, indicating, or backlighting different types of stationary and mobile display devices, such as large scale advertising display boards and residential lighting, all the way down to small cellular telephone displays. In such applications, many designers and manufacturers are using light emitting diodes (LEDs) because LEDs have many performance and cost advantages over other available light source technologies. Such advantages include greater reliability, lower power consumption, lower maintenance requirements, and lower costs, and have contributed to a significant increase in the use of LEDs in many industries.
This upward trend in using LEDs for lighting applications have been further bolstered by various advances in LED design and manufacturing that have led to even longer usable life, greater energy savings, better quality light, higher safety, smaller and more versatile packages, and greater durability. All of these advantages have contributed to the increased use of LEDs in residential and commercial lighting applications. However, to fully replace legacy dimmable light sources, such as incandescent light sources, LEDs often require the use of retrofits of dimmers and other control circuitry for controlling the light output level of the LEDs.
Many dimmers currently implemented and installed are based on bidirectional triode thyristors or bilateral triode thyristors, commonly known in the industry as a triode for alternating current (TRIAC) devices. Such TRIACs can conduct current in either direction when triggered, or otherwise turned-on, and are commonly used in many low power applications, such as light dimmers, speed controls for electric motors, and in many other household appliances.
One prevalent uses of TRIACs is in dimmers for incandescent lamps. FIG. 1 shows a simplified schematic of a conventional TRIAC based dimmer for use in various lighting applications. The particular example of the TRIAC based dimmer 100 shown in FIG. 1 can be used to manually set the light output level of a tight source to customize the light level or energy consumption. The TRIAC 110 can be coupled to an alternating current (AC) source 105 and a bridge diode 115. The AC source 105 can operate at various frequencies and voltages ranges. Typically the frequency and voltage ranges are standard and set by government or other regulating bodies. For example, in North America, household power is supplied at 50-60 Hz with voltages in the range or 110-130V. Bridge diode 115 can be coupled to a light source, such as lamp 120 of an appropriate rating based on the light requirements and the specifications of the AC source 105.
To change the output level of the lamp 120, the TRIAC 110 can be used to chop the current on the leading or trailing edge of the AC source 105, as shown in FIG. 2. Leading edge dimmers, such as TRIAC dimmers, essentially remove, or chop, some portion of the AC current 220 by only conducting the input current 230 when the input voltage reaches a certain threshold level 210A on the leading edge of the current signal, as shown in graph 200A. In contrast, trailing edge dimmers chop some portion of the AC current 220 by only conducting the input current 230 until the input voltage reaches a certain threshold level 210B on the trailing edge of the current, as shown in graph 200B. Such augmented input signals are thus referred to as being “chopped” because there are periods in the rising or falling edge of the input signal in which the signal is cut-off. The cut-off portions of the input signal represent the periods when the dimmer is non-conducting. As the chopped AC current 220 is integrated overtime, less current is delivered to a lamp than would be if the input current 230 was delivered to the lamp, and therefore the lamp appears less bright.
In similar implementations, a TRIAC based dimmer can be biased or controlled with a radio frequency (RF) signal to provide some portion of the rising edge input AC current to produce an output AC current 300 with a profile like the one shown in FIG. 3. During the RF bias conduction periods 315A and 315B, the input signal is conducted by the TRIAC to deliver the rising edge portions 310A and 310B of the input current, as shown. Accordingly, the AC current can be chopped at various times during the rising edge to produce specific AC current profiles to a component, light source or lamp.
Unfortunately, the use of TRIAC dimmers is not particularly compatible with many of the retrofit LED modules coming onto the market in anticipation of the phase of incandescent light bulbs and lamps. Most conventional legacy TRIAC dimmers expect to see some resistive load, such as an incandescent lamp, however, most LED circuits present a capacitive and inductive load to the legacy TRIAC dimmer, rendering them mostly incompatible. Embodiments of the present disclosure are directed toward systems, apparatus and methods for detecting the use and effects of a TRIAC based dimmer so that it can be effectively used to dim and control a LED light source.